This invention relates to the dehydration of halogenated unsaturated alcohols to form the corresponding halogenated conjugated dienes.
The dehydration of unsaturated alcohols to form conjugated dienes is well-known. However, reaction conditions which give good results with nonhalogenated unsaturated alcohols, when used with halogenated unsaturated alcohols, can allow polymerization, isomerization, rearrangements, and other undesired side reactions. These reactions compete with the production of the halogenated diene and thus cause low yields and an impure product.
It is known to dehydrate nonhalogenated unsaturated alcohols by contacting them, in the vapor phase, with a catalyst in the presence of steam. See, e.g., U.S. Pat. Nos. 3,657,376 and 4,049,736.
U.S. Pat. No. 4,078,008 discloses the formation of 1,1-dichloro-4-methyl-1,3-pentadiene in yields of up to 88 percent by the dehydration of 1,1-dichloro-4-hydroxy-4-methyl-1-pentene. All examples show liquid phase reactions.
U.S. Pat. Nos. 4,081,488 and 4,216,173 disclose the dehydration of 1,1-dichloro-3-hydroxy-4-methyl-1-pentene to form 1,1-dichloro-4-methyl-1,3-pentadiene in yields of up to 89 percent using dehydrating catalysts such as activated clay, aluminum oxide, and aluminum silicate. All examples show liquid phase reactions.
British Pat. No. 1,528,119 and British Pat. No. 1,554,690 disclose the gas phase dehydration of 1,1-dichloro-3-hydroxy-1-butene with an aluminum oxide catalyst to form 1,1-dichloro-1,3-butadiene in about 90 to 92 percent yield.
Bull. Chem. Soc. Jap., Vol. 40, pp. 1991-2, (1967) discloses the liquid phase dehydration of 1,1,2-trichloro-3-hydroxy-1-butene to give yields of up to 51 percent of 1,1,2-trichloro-1,3-butadiene.
U.S. Pat. No. 3,483,263 discloses the gas phase dehydration of 1,1,2-trichloro-3-hydroxy-1-butene over activated alumina to form the diene in about 73 percent yield.
The prior art processes tend to require the use of an inordinate amount of catalyst. In many cases one part by weight of catalyst does not convert even one part by weight of alcohol. The prior art methods leave room for improvement in conversion, selectivity, yield, catalyst efficiency, or any combination of these. Thus, it would be highly desirable to possess a process for the production of halogenated conjugated dienes, especially the highly reactive tri-halogenated dienes, which would provide some or all of the improvements listed above.